The present invention broadly relates to circuit breakers or interrupters and pertains, more specifically, to a new and improved gas-blast circuit breaker.
Generally speaking, the gas-blast circuit breaker of the present invention performs a closing operation and an opening operation to assume a closed-circuit position and an open-circuit position, respectively, and is of the type comprising a stationary contact piece and a movable contact maker which are arranged in an ambient space comprising a quenching gas. The movable contact maker is provided with an axial passage starting at the free end of the latter and is encompassed by a blast nozzle which in the closed-circuit position is penetrated by the stationary contact piece. The port of the blast nozzle communicates with a pumping space which can be pressurized during an opening stroke and is delimited by a pumping cylinder and a pumping piston, whereby the axial passage at the end remote from the free end of the movable contact maker opens into a blow-out space which is delimited by a cylinder and a piston, the latter being operatively associated with the movable contact maker. The blow-out space is connectable with the ambient space during the closing operation by means of controlled valve means.
Such type of gas-blast circuit breaker is known, for instance, from European Patent Application No. 0,380,907, published Aug. 8, 1990. In the circuit breaker disclosed therein, the quenching gas flowing into a blow-out space assists the driving mechanism during the interruption of relatively high-amperage currents. In order to avoid, during the closing operation, an overpressure requiring additional driving effort of the driving mechanism, there are provided cylindrical slide-valve means which during the closing stroke, as a result of the thereby generated relatively high excess pressure in the blow-out space with respect to a slight negative pressure in the pumping space, release radially extending openings provided in a cylinder delimiting the blow-out space, so that excess pressure can vent through the radially extending openings and thus ensure pressure compensation between the blow-out space and the ambient space or gas plenum. In order to control the slide-valve means, there is provided a control piston in the pumping piston separating the pumping space from the blow-out space. In order that the driving mechanism need not provide more driving energy during the interruption of relatively low-amperage currents than in a circuit breaker without a blow-out space, a piston delimiting the blow-out space and operatively associated with the movable contact maker is provided with a large-surface check valve, the latter remaining open because the pressure increase due to the established arc is insufficient to press the valve body or disk against its seat.
This known gas-blast circuit breaker is not only disadvantageous in that a certain requisite pressure difference between the pressure in the pumping space and the pressure in the blow-out space has to be first built up, in order to open the aforesaid slide-valve means, such pressure difference build-up requiring driving energy, but also for the reason that --at the start of the downward opening or tripping stroke--the slide-valve means have to be first brought again to the closed position thereof, whereby the pumping space is enlarged by the thereby effected displacement of the control piston. As a result, the generated pressure in the pumping space is decreased, thus impairing the interrupting capacity of the circuit breaker. Furthermore, slide-valve means as provided in the prior art construction require a corresponding constructional expenditure and substantially increase the manufacturing costs of the circuit breaker.